On-board oxygen booster for peak power in fuel cell systems

ABSTRACT

Recognizing the fact of extremely low utilization of peak power (especially in the aviation use case), we propose a novel approach to significantly reduce the size and weight of the system by downsizing the main air compressor to match the air flow required to produce the desired continuous power (e.g., 55% of the peak power rating for the aviation applications, etc), and provide the supplemental oxygen flow from an on-board high-pressure oxygen tank.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This regular U.S. patent application relies upon and claims the benefit of priority from U.S. provisional patent application No. 62/808,309, entitled “ON-BOARD OXYGEN BOOSTER FOR PEAK POWER IN FUEL CELL SYSTEMS,” filed on Feb. 21, 2019, which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The disclosed embodiments relate in general to clean energy based air transportation systems technology, and, more specifically, to on-board oxygen booster for peak power in fuel cell systems.

Description of the Related Art

In today's high performance fuel cell systems, oxygen supply is one of the most serious performance bottlenecks. At peak power output, a very significant amount of air needs to be supplied to the fuel cell—for example, in one 125 kW fuel cell system, over 500 kg of air needs to be supplied per hour at high pressure. The current state of the art in the industry is to use electric motor-driven compressors to provide such flows to achieve peak power. These compressors are extremely expensive and heavy, resulting in significant degradation of the overall system performance per unit of weight.

SUMMARY OF THE INVENTION

The inventive methodology is directed to methods and systems that substantially obviate one or more of the above and other problems associated with conventional technology.

In accordance with one aspect of the embodiments described herein, there is provided a method for providing on-board oxygen booster for peak power in fuel cell system, the method comprising downsizing the main air compressor to match the air flow required to produce the desired continuous power (e.g., 55% of the peak power rating for the aviation applications, etc), and providing the supplemental oxygen flow from an on-board high-pressure oxygen tank.

Additional aspects related to the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Aspects of the invention may be realized and attained by means of the elements and combinations of various elements and aspects particularly pointed out in the following detailed description and the appended claims.

It is to be understood that both the foregoing and the following descriptions are exemplary and explanatory only and are not intended to limit the claimed invention or application thereof in any manner whatsoever.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the inventive technique. Specifically:

FIG. 1 depicts one of the possible embodiments.

DETAILED DESCRIPTION

In the following detailed description, reference will be made to the accompanying drawing(s), in which identical functional elements are designated with like numerals. The aforementioned accompanying drawings show by way of illustration, and not by way of limitation, specific embodiments and implementations consistent with principles of the present invention. These implementations are described in sufficient detail to enable those skilled in the art to practice the invention and it is to be understood that other implementations may be utilized and that structural changes and/or substitutions of various elements may be made without departing from the scope and spirit of present invention. The following detailed description is, therefore, not to be construed in a limited sense.

We observe that in most of the fuel cell applications the peak power needs to be produced rather infrequently. For example, in aviation applications, peak power needs to be produced only for 2 minutes per flight—during the initial takeoff roll and 1,000-foot climb, before the power levels are reduced to 85% or lower. Similarly, in automotive applications, maximum power is requested from the system only during the times of heavy acceleration and such periods generally last less than 10 seconds, and applied perhaps every few minutes of driving. Therefore, maximum power is requested from the system only for 1-2% of the time (aviation) or 3-5% of the time (automotive).

Oxygen Tank

Recognizing this fact of extremely low utilization of peak power (especially in the aviation use case), we propose a novel approach to significantly reduce the size and weight of the system by downsizing the main air compressor to match the air flow required to produce the desired continuous power (e.g., 55% of the peak power rating for the aviation applications, etc), and provide the supplemental oxygen flow from an on-board high-pressure oxygen tank.

Oxygen from the supplemental tank is then mixed in on demand with compressed air from the main compressor (that is now substantially smaller and lighter), based on the signal from the main powertrain control unit (PCU). PCU signal specifies the target O2 partial pressure to the mixing/pressure-regulating device to arrive at the right oxygen flow to support the target power level.

An additional component of such new system could also be an oxygen recirculation system that would capture exhaust air from the fuel cell output (which still has some remaining oxygen) and direct it back to the ambient air input of the system. Such a system would be especially useful if very high oxygen concentrations are requested by the PCU and the concentration of oxygen in the fuel cell exhaust is correspondingly higher.

The supplemental oxygen supply proposed in this invention could be stored in the standard on-board composite cylinder tanks with similar molar density as the H2 storage already present in the system. In aviation application example, a system operating at 125 kW peak power for 2 minutes and 70 kW continuous power for 90 minutes, would require only 2 kg of usable supplemental O2. A readily available today's technology allows to store such amount of oxygen in a tank with empty weight of about 4 kg. Therefore, the complete oxygen booster system, including the proposed air-oxygen mixing system, would weight less than 8 kg. For comparison purposes, a commonly used battery power/energy buffers would weigh at least 50 kg and require complicated electronics (battery management system). As can be seen, the novel proposed approach would result in 6-fold reduction of weight compared to the current state-of-the-art.

Compressed Air Tank

In addition to auxiliary oxygen tank a compressed air tank can be used to substitute air compressor function at initial fuel cell startup process. In order to start the fuel cell system electric power is required to start the main air compressor. This initial power requirement varies, possibly up to 20 kW. This requires the presence of a high voltage battery pack for starting the fuel cells. In order to avoid using high voltage battery pack (due to weight and system complexity) an auxiliary compressed air cank can be used. At the initial fuel cell start up stage this take will replace compressor function and will supply compressed air at given pressure and flow rate until fuel cell voltage raises to the level high enough to drive an air compressor. This will allow the start of the fuel cell system without a high voltage battery pack at the ground as well as in the air in case of emergency shut down/restart procedure. Existing high pressure air tanks made of composite materials will significantly reduce the weight of the system compared to high voltage batteries. In order to maintain pressure in the air tank a relatively small and lightweight compressor can be used because charging rate for such a system does not have to be high (compressed air is only used during system start up).

FIG. 1 depicts one of the possible embodiments.

Finally, it should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. It may also prove advantageous to construct specialized apparatus to perform the method steps described herein. The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive.

Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination in aircraft power plants. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 

What is claimed is:
 1. A method for providing on-board oxygen booster for peak power in fuel cell system, the method comprising downsizing the main air compressor to match the air flow required to produce the desired continuous power (e.g., 55% of the peak power rating for the aviation applications, etc), and providing the supplemental oxygen flow from an on-board high-pressure oxygen tank. 